An extended-range electric vehicle or EREV generally provides an extended electric-only (EV) series propulsion mode. In a series hybrid system, an electric machine attached to the engine functions as an electric motor to start the engine, and allows the electric machine, or a separate electric machine attached to the remainder of the drive train, to selectively act as a generator and thereby recover energy into a battery. A series design has an increased weight due to the electric machinery necessary to transform all engine power from mechanical-to-electrical and from electrical-to-mechanical, and from useful power lost in this double conversion. Additionally, series designs lack a direct mechanical path between the engine and the drive wheels.
An EREV has an onboard battery that can be recharged via plug-in battery power as well as via regenerative braking. The onboard gasoline engine turns an electric generator as needed to provide the extended EV operating range. Once the battery is largely depleted, the EREV design continues to extend the EV operating range of the vehicle as long as fuel remains in the tank. For commutes shorter than a threshold distance, e.g., approximately 40 miles in some embodiments, the engine is not required at all, and all propulsion is provided in EV mode.